Atomically precise graphene nanoribbon heterojunctions from a single molecular precursor

Abstract

TitleAtomically precise graphene nanoribbon heterojunctions from a single molecular precursor AbstractThe rational bottom-up synthesis of atomically defined graphene nanoribbon (GNR)heterojunctions represents a key enabling technology for the design of nanoscale electronic devices. Synthetic strategies have thus far relied on the random copolymerization of two electronically distinctive molecular precursors to yield a segmented band structure within a GNR. Here we report the fabrication and electronic characterization of atomically precise GNR heterojunctions prepared through a late-stage functionalization of chevron GNRs obtained from a single precursor that features fluorenone substituents along the convex edges. Excitation of the GNR induces cleavage of sacrificial carbonyl groups at the GNR edge, thus giving rise to atomically well-defined heterojunctions comprised of segments of fluorenone GNR and unfunctionalized chevron GNR. The structure of fluorenone/unfunctionalized GNR heterojunctions was characterized using bond-resolved STM (BRSTM) which enables chemical bonds to be imaged via STM at T = 4.5 K. Scanning tunneling spectroscopy (STS) reveals that the band alignment across the interface yields a staggered gap Type II heterojunction and is consistent with first-principles calculations. Detailed spectroscopic and theoretical studies reveal that the band realignment at the interface between fluorenone and unfunctionalized chevron GNRs proceeds over a distance less than 1nm, leading to extremely large effective fields.

Orbitally Matched Edge-Doping in Graphene Nanoribbons

“…The corresponding data for unfunctionalized cGNRs is provided as a reference. 33 When compared to pristine cGNRs, the introduction of O-dopant atoms leads to a significant shift of the conduction band (CB) edge to lower energies while the valence band (VB) edge remains essentially unperturbed. This is reflected in a reduction (~0.2 eV) of the band gap of O-doped cGNRs to 2.3 eV.…”

Finding the hidden valence band of N = 7 armchair graphene nanoribbons with angle-resolved photoemission spectroscopy

“…Graphene nanoribbons (GNRs) have a band gap and a tunable electronic structure, and therefore they are a promising material for opto-electronic applications. After the discovery of bottom-up synthesis which allows atomically precise fabrication [1], there is a boom in design and study of GNRs [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. The first reported [1] and the most studied system is the semiconducting armchair graphene nanoribbons of N = 7 carbon atoms width (7-AGNRs).…”

Substrate-molecule decoupling induced by self-assembly—Implications for graphene nanoribbon fabrication

“…The other scheme (the 'radical coupling scheme') involves forming a covalently-bonded polymer structure from precursor self-assembly, which transforms into graphene nanoribbon upon being heated. [27][28][29][30][31][32] The radical coupling scheme, which occurs due to carbon-halide bond cleavage within the precursor molecules upon deposition, has been confirmed for a wider range of substrates and precursor molecules compared to the self-assembly scheme. However, the self-assembly scheme is arguably more flexible than the radical coupling scheme, because a greater variety of supramolecular structures (and hence graphene nanoribbon types) are available compared to covalently-bonded structures.…”